/Engine/Plugins/FX/Niagara/Source/Niagara/Classes/NiagaraGPUInstanceCountManager.h
Resize instance count and draw indirect buffers to ensure it is big enough to hold all draw indirect args.
void ResizeBuffers ( [FRHICommandListImmediate](API\Runtime\RHI\FRHICommandListImmediate) & RHICmdList, int32 ReservedInstanceCounts )